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Discussion Starter · #1 ·
OK, I will admit to being a 75% video, 25% audio enthusiast. However, this HD audio mess is really starting to freak me out... I spent the day watching some movie and music clips to get a feel of the differences between different formats. During this, I came across a really strange issue with the LFE level of TrueHD playback. This may get a bit long, so I apologize in advance for that...


The setup (not my own personal setup, just what I happened to have available): Onkyo TX-SR605, PS3, Samsung BDP-1400 BD player (MK Sound speakers - irrelevant for this discussion). What I found out was that when playing Celine Dion - A New Day in TrueHD, there was a difference in LFE level between the two players. At first, it seemed obvious to me that this would be the "usual" issue of the receiver not elevating the LFE channel the required 10 dB - the LFE when using bitstream from the Samsung was 10 dB low compared to using PCM from the PS3, and it was fairly obvious that the PS3 delivered the correct LFE level, while the Samsung had way too low LFE. But then I started doing a bit of testing.


What I found was, that if I set the Samsung to output PCM, the issue was still there. This can mean one of two things: The issue is in the player - which shouldn't be possible, given that it's a bitstream output, but who knows (I didn't have another player with bitstream output at hand, I'll get back to it when I do). Or, the issue is in both, so when the player is decoding, it's doing the same mistake... Not very unlikely, given that it's fairly cheap equipment. I've read about similar issues with other Onkyo models, and I wouldn't trust Samsung much in this regard either.


However, then I started testing some more with other discs, and then the weird part begins... I played back The Dark Knight, and the re-issue of The 5th Element (it was the only disc at hand with both TrueHD and PCM). NEITHER of theses had the LFE issue that was very apparent with the Celine Dion disc! I've spent 3 hours flipping back and forth, and there's no doubt about it - when playing the TrueHD 5.1 track on the Celine Dion disc, there is a very obvious difference in the LFE level, when playing the TrueHD 5.1 track on TDK and 5th Element, there was not! I have measured the output from the sub using a radioshack, and there is no difference on those discs, but a clear 10 dB diff. on Celine Dion. I tried setting the speakers to Large instead of 80 Hz crossover, but that didn't make any difference. The speaker setup in the player was Large all round, but that shouldn't affect bitstream output anyway.


How on earth is this possible? Are there any ways to differentiate the way a TrueHD track is decoded/encoded (other than Dialnorm, which shouldn't affect LFE relative to the other channels - right?) It seems there are things going on when decoding a TrueHD signal, that doesn't quite seem obvious. Whether it's the player or the receiver making the error, I simply can't get my head around how it's not consistent from disc to disc. There must be some kind of difference between those TrueHD signals, that I'm missing?


Anyway, long story short: We need HD audio test signals, and lots of'em! We have DD and DTS test signals, for instance on the Digital Video Essentials DVD, so it's fairly easy to check whether or not the receiver is doing it's job right when decoding DD or DTS signals - but to my knowledge there aren't any TrueHD, DTS-HD or multichannel PCM test signals easily available anywhere? It seems one would need not only signals in different formats, but in different variants of each format too!


I don't know anything about authoring tools at all, but is there any realistic chance of starting an AVS HD Audio project, like the AVS709 video test discs? Is it even possible to make your own TrueHD and DTS-HD audio tracks?


BTW, for some reason it seems the TX-SR605 consistently plays back PCM signals 3-4 dB lower than bitstream signals, so when testing I measured the near-field output of one of the speakers and adjusted accordingly, before measuring the sub output - so it shouldn't make a difference to this issue. However, it is something to consider if one is trying to listen to the difference between decoding in the player vs decoding in the receiver.
 

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I am not, at all, an authority on any A/V stuff, but I would think the logical deduction here is that MAYBE the low freqs in the Celine Dion disc are not actually in the LFE channel data. The reason I suggest this is with the thought of removing the PS3 from the observation. By setting the receiver to Large speakers, it is possible that it will not automatically divert the lows to the LFE channel. This is very reproducible for me. I have large speakers in the fronts, but must set the receiver (HTR-5790) to 'Small' in order for it to send non-LFE lows to the LFE output. That would absolutely explain your condition, again excluding the fact that the Sony PS3 seems to work fine.


Give it a try......
 

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Discussion Starter · #3 ·

Quote:
Originally Posted by Colby Burkett /forum/post/15549801


I am not, at all, an authority on any A/V stuff, but I would think the logical deduction here is that MAYBE the low freqs in the Celine Dion disc are not actually in the LFE channel data. The reason I suggest this is with the thought of removing the PS3 from the observation. By setting the receiver to Large speakers, it is possible that it will not automatically divert the lows to the LFE channel. This is very reproducible for me. I have large speakers in the fronts, but must set the receiver (HTR-5790) to 'Small' in order for it to send non-LFE lows to the LFE output. That would absolutely explain your condition, again excluding the fact that the Sony PS3 seems to work fine.


Give it a try......

Thanks for the input (I guess I should maybe try in the receiver area, this area doesn't seem to attract too many readers...). I had the same thought and I already tried with the receiver on both small and large for all speakers, the result was the same. Also, with the PS3 doing the conversion and the receiver on Large for all speakers, there was full LFE output, so it doesn't seem to be the explanation.


But I see what you were getting at, and on 5th element there was very little information in the LFE channel, on that one there was a big difference between small and large setting, but no difference between bitstream and PCM. That's why I slipped in TDK afterwards, to make sure that there was info in the LFE, but I'm very sure that the bass info on the Celine Dion disc contains quite a lot of LFE info.


UNLESS - which is why I wanted test signals! - the PS3 is doing it's own bass management... That MAY explain things actually, but how do we find out, when we have no test signals?
 

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Discussion Starter · #4 ·
I'll dig up this thread again, as I'm quite dissapointed that noone seems to think that the lack of HD audio test signals is an issue. I think this is a HUGE issue that needs to be addressed. Sadly, I don't have the knowhow to create such signals, but I do feel that it's needed. I had an experience with a Panasonic BD50, which apparently can't deliver a 7.1 PCM signal as PCM. My next thought was to try to figure out what happens to the last two channels, because subjectively it sounded like they were simply skipped. Once again, I found that it is basically impossible to find actual test signals in DTS-HD, Dolby TrueHD and PCM 7.1 form.


Seriously, with these new formats we've opened up an incredible amount of new possibilities to mess things up. Why doesn't anyone seem to think that we need a simple set of test signals, to make sure everything is handled correctly throughout the audio chain?
 

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Some people think there is an association between Celine Dion and the movie Videodrome.
 

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Maybe I'm missing something, but if this doesn't happen with both of your players, how would having HD audio test tones alleviate your problem?


The SD tones worked well enough with the PS3.
 

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Quote:
Originally Posted by Otto J /forum/post/15527452


clear 10 dB diff. on Celine Dion.

I found a way to make a nearly 100dB improvement on sound quality with all Celine Dion discs; turn them off.


I agree with the other posters about trying via the AVR where you will have more options setting the audio to help diagnose the problem.
 
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